Various approaches to ensuring circuit integrity have been proposed and certain of these circuits are described, by way of example, in the following described patents:
Bliven et al. U.S. Pat. No. 5,111,497, issued May 5, 1992, and assigned to Raychem Corporation, discloses an alarm and test system for apparatus that transmits and receives multiple telephone transmission signals over a single twisted pair wire. A digital main line system is provided that includes a line card at central office facilities and a remote terminal at a subscriber station. Multiple signals can be transmitted in digital form from the line card to the remote terminal location. The line card converts conventional analog signals to 2B1Q signals for transmission and the remote terminal converts the signals back to analog for use with conventional subscriber equipment.
A remote terminal emulator, having a predefined data pattern, may be provided at the central office facilities. As a means for detecting line card failures, comparison is made of a response of the line card with the emulated output. The test system may include a voltage source current monitor attached to the twisted pair to detect failures in the twisted pair and generate ring and test request voltage for checking parts of the line card. Failures at the remote terminal may be detected by providing a line card emulator.
Various other testing functions may be provided. A voice frequency emulator, connected to the line card or line card emulator, may be included to convert to a digital signal for transmission over the twisted pair to the remote terminal. The function of the line card, the twisted pair or the remote terminal, can be evaluated by measuring a returned amount of noise or reflected signal. Further testing procedures include testing digital-to-analog conversion equipment at the remote terminal and testing of a ring signal at the remote terminal.
Also disclosed is the structural arrangement of the remote terminal enclosure. Various test access ports, sockets and plugs are depicted.
Seo U.S. Pat. No. 4,446,551, issued May 1, 1984 and assigned to Kabushiki Kaisha Meidensha, discloses a data transmission system having two transmitting line loops connecting a master station and a plurality of remote slave stations. The system can detect a portion of a line where a break or equivalent malfunction occurs and form a loop back to permit continuation of the transmission function.
The master station transmits signals in opposite directions to the first and second lines. Each remote station and master station captures or relays and generates data received, as transmitted through the first and second transmitting lines. The remote station responds to the received information and transmits the information contained in the data signal to the neighboring station. The method of data transmission involves interrupting the relaying and generating in the first transmitting line, and shifting a gate. Each station comprises one serial/parallel converter circuit. Each station has two sets of transmitters and receivers responding to the dual transmitting lines. Each remote station has two sets of retrigger timers having different durations and responsive to the first and second transmitting lines to determine whether or not a transmitting signal exists.
In the event of a break in a transmitting line, there is a shift in the output status of a timer in a station connected with the line. In response to the shift, dummy data are transmitted to the neighboring station remote station. All remaining remote stations beyond the break are placed in a non-signal condition. The remaining stations time out and shift back to the original output status as dummy data has been transmitted. The station connected to the line break does not shift back since there has been no data transmitted thereto due to the line break. The master station can thus recognize the location of the line break and form a loop back for data transmission without the section of line including the break.
Bachhuber et al. U.S. Pat. No. 5,036,318, issued Jul. 30, 1991, and assigned to Siemens Aktiengesellschaft, discloses a modularly structured comprehensive ISDN communication network which includes multiple test facilities. Included are a centrally located through-connection module which comprises a digital switching matrix array and a central control device, and operation and data modules at peripheral system locations that fulfill specific tasks by means of individual program controls using multi-processor arrangements.
Special hardware and software modules assure that various components of the system are in a constant ready state. Testing objectives include trouble recognition, trouble localization, trouble evaluation and trouble reports. A dependability sub-module, which is specifically adapted to hardware structure and program operation, is provided for each module. A hierarchy is established among the various dependability sub-modules in the system, the through-connection module having central significance.
The central system dependability systems sub-module is provided with error outputs from the individual sub-modules. The error outputs include texts indicating type of error, location of error and, if possible, cause of error. Particulars may be included, such as point in time of the occurrence of an error, initiated or recommended recovery measures, or error-explaining auxiliary data which are either hardware-oriented or software-oriented. Arbitrary user-specified text signals can be generated and outputted. Error reports are compiled based on defined ordering criteria. Display of error information is available at arbitrary error output equipment in prioritized fashion.
West U.S. Pat. No. 4,491,838, issued Jan. 1, 1985, and assigned to IBM, discloses a multiterminal processing system including a digital communication network with a digital switch as its central terminal in a star configuration. Input from each terminal is switched back to the next terminal in the loop network. Activity in the loop is monitored at the digital switch. In the event of a failure, the monitor can determine the failing terminal in the loop by use of a binary search around the loop. A loop failure is automatically isolated and bypassed. The starloop switch can configure subsections of the network into point-to-point, star, or multipoint modes.
Cookson et al. U.S. Pat. No. 4,551,718, issued Nov. 5, 1985, and assigned to Tetragenics, Inc., discloses a communication system for transmitting, over a single communication channel, status information relating to each of a plurality of power devices in an electrical power distribution system. At each location a monitoring device is provided for monitoring the state of a plurality of relays or other devices that are capable of being in either an active or inactive state. A digital signal representative of the monitored states is produced and processed for transmission. A receiver at a second remote location compares the transmitted information with a stored table to verify the validity of the coded information. If invalid, an alarm signal is generated at the second location and maintained until a valid code is received.
Steinke U.S. Pat. No. 4,774,510, issued Sep. 27, 1988, and assigned to Electrocon, Inc., discloses a monitoring annunciator apparatus for centralized monitoring of remotely positioned alarm contacts in order to permit a control room operator to visually scan a display panel to assess the status of the monitored alarm points. The apparatus utilizes a single signal wire for each monitored contact point and a ground wire common to all monitored contact points to provide notification through separate audible and visual indication of both the occurrence of a change in the status of each monitored field contact point, through the issuance of a contact alarm, and an indication of the occurrence of a change in the integrity of each wire pair, through the issuance of a line alarm, and implementation of corrective measures to return the field contact points and associated wire pair to normal status.
Steely U.S. Pat. No. 4,841,520, issued Jun. 20, 1989, and assigned to AMP Incorporated, discloses a data transmission system which utilizes multiplex techniques to transmit data signals among interface circuits. A central controller is coupled to a bus and applies clock signals thereto. The controller also receives data signals from the bus and applies data signals to the bus. A plurality of remote stations are coupled to the bus. A first such remote station counts the clock signals and can apply first a data signal to the bus during a time period corresponding to a first selected count. A second such remote station counts the clock signals and can receive a second data signal from the bus during a time period corresponding to a second selected count.
A fault detection system is provided to detect a failure of the bus and, in response thereto, prevent the clock signals from being transmitted to the second remote station. A plurality of parallel buses may be provided from the central controller, each to a respective subset of the remote stations. If an individual bus fails clock pulses are prevented from being carried to the subset associated with the failed bus.
While the above described systems address similar problems the solutions are dependent on comprehensive systems not readily or economically available at the present time.